This invention relates to electronic printed circuit card cage assemblies, and more particularly, it relates to a modularized electronic card cage interfacing assembly for use in a telex switching system for interfacing the electrical connections between customer termination leads and the input-output pins of the printed circuit card edge connectors.
In electronic systems which use printed circuit boards to contain the various electrical components and to interconnect them to achieve the desired functions, there is often a need to make electrical connections between the card edge connector input-output pins, which provide the electrical connections between the circuits on the printed circuit card and the rest of the system, and an external device (customer termination). The wires used in the interconnections between the various printed circuit card edge connector pins contained in the electronic card cage assembly are selected to be compatible with the particular type of pins the card edge connectors have, such as wire-wrap pins. That is, if a wire-wrap pin is provided on the card edge connector, the appropriate sized solid interconnect wire will be used to make the electrical interconnections. However, the customer termination wires may range in types from multiple conductor (stranded) wire of varying conductor sizes to single conductor (solid) wire of similar sizes, and these wires must be connected to the input-output pins of the card edge connectors, a connection in which the wire sizes may not be compatible to the pin sizes. For example, a size 20 gauge stranded wire cannot easily be connected to a 0.025 square inch wire-wrap pin which usually requires a 30 gauge solid wire.
Accordingly, making these customer termination lead connections to the backplane pins of the card edge connectors is a difficult problem. For example, the larger gauge stranded wires cannot be wire-wrapped to a wire-wrap post. For best results, they should be soldered. The bulkier wires produce solder joints on the connection pins that can result in shorts between adjacent wire-wrap posts if care is not taken to insulate the connection. Additionally, changes in termination connections are difficult to make when the termination lead has been soldered to a wire-wrap post. Soldering a stranded wire to a wire-wrapped post usually results in the lower wire-wrapped interconnection leads between the various card edge connectors becoming soldered to the post. This in effect makes those connections permanent, and if a change is needed, it is difficult to remove them.
A further problem in making the special customer termination connections to the input-output pins of the card edge connectors results from the need to have special purpose interface circuits, such as loading resistors, RC filters, capacitors, etc., inserted in the customer termination leads. These circuits may be required by such things as a need to match the source impedance to the load impedance, whether the source is in the card cage or is in the customer's equipment. And is often the case, there is no convenient place available for providing these circuits.
An additional problem presents itself in providing a means to support the wire bundle created from the customer termination leads as the leads are distributed to the various input-output pins of the card edge connectors. These termination leads need to be supported so that the weight of the wires does not pull at the electrical connection between the lead and the pin.
Therefore, it would be desirable to provide a way to interface the special customer termination leads to the input-output pins of the printed circuit card edge connector pins, such as through soldering to insure a strong and electrically sound termination connection, regardless of the type or size of termination wire used, or of the type or size of the card edge connector pins used. The interfacing assembly should provide a way to support the customer termination leads so that the weight of the bundle of wires will not damage the termination connections. Further, the interfacing assembly should provide an easy way to make changes in the termination connections as the customer requirements change, and to make these changes, the customer termination connections as well as the input-output pin connections should be accessible from the rear of the card edge connector assembly. In addition to the foregoing considerations, the interfacing assembly should be modular in construction so that if a full interface assembly is not required, less than a full unit can be provided, and as the customer requirements change, it can be expanded. Also, if there is damage to part of the assembly, the damaged part can be easily changed without having to replace the entire assembly.